1. Field of the Invention
The invention relates to a vehicle that includes a three-phase alternating-current motor, an electrical storage unit that is able to exchange electric power with the three-phase alternating-current motor via an inverter, a smoothing capacitor that smoothes voltage between the inverter and the electrical storage unit and a collision detecting unit that detects a collision of the vehicle, and also to a control method for the vehicle.
2. Description of Related Art
There is suggested a vehicle of this type, which includes a motor generator, an inverter circuit that drives the motor generator, a secondary battery unit that supplies electric power to the inverter circuit via a system main relay, a high-voltage capacitor that is provided between the system main relay and the inverter circuit and a radar sensor that measures the relative speed between an obstacle and the vehicle and the distance between the obstacle and the vehicle (for example, see Japanese Patent Application Publication No. 2005-20952 (JP-A-2005-20952)). In this vehicle, when a collision of the vehicle is predicted on the basis of information from the radar sensor, the system main relay is turned off, the inverter circuit is controlled so as to discharge the electric charge remaining in the high-voltage capacitor using coils of the respective phases of the motor generator while torque is not generated from the motor generator. In addition, there is suggested a vehicle of this type, which includes a motor generator, an inverter that has pairs of serially connected upper arm transistor and lower arm transistor and that drives the motor generator and a capacitor that is provided between a direct-current power supply and the inverter, and in which, when there occurs a short-circuit failure in any one of the upper arm and lower arm transistors of the inverter, the vehicle is caused to stop running, and the upper arm or lower arm transistor serially connected to the upper arm or lower arm transistor that has a short-circuit failure is turned on to fix the upper and lower arms of the short-circuit phase in a conductive state to thereby consume the electric charge stored in the capacitor as a short-circuit current (for example, see Japanese Patent Application Publication No. 2008-54420 (JP-A-2008-54420)). In this vehicle, when there occurs a short-circuit failure in the inverter as described above, the upper and lower arms of the short-circuit phase are fixed in a conductive state to form a path that passes current, in addition to a closed circuit between the motor generator and the inverter, to thereby prevent an overcurrent state of the inverter or conductive line even when large counter electromotive force is continuously generated in the motor generator, for example, while the vehicle is being towed.
Incidentally, in a vehicle of this type, when a collision actually occurs, the electric charge stored in the capacitor between the direct-current power supply and the inverter should be promptly discharged in terms of ensuring safety. However, when the upper and lower arms of the inverter are fixed in a conductive state after occurrence of a collision of the vehicle by applying the invention described in JP-A-2008-54420, large current flows through the upper and lower arms fixed in a conductive state, so there is a concern that the transistors may be adversely influenced. Furthermore, when counter electromotive force is generated in the motor generator, current discharged from the capacitor and current resulting from the counter electromotive force flow at the same time, so there is a concern that the transistors may be adversely influenced. In addition, when current resulting from the counter electromotive force is returned to the motor generator via the inverter and half-wave current flows through the phases of the motor generator, a permanent magnet of the motor generator may possibly be demagnetized.